1. Field of the Invention
The present invention relates generally to a lens drive mechanism of an auto-focusing camera, and more particularly to a drive mechanism of an auto-focusing camera with built-in camera lens.
2. Description of Related Art
Usually we need a camera to record memorable moments. The designs of cameras have evolved toward lightweight and compactness, so have the currently popular digital cameras. Conventionally, an auto focus structure is used for controlling the telescopic movement of a lens of the camera.
The auto focus structure of the camera focuses on an object by comparing with the image on an image sensor which is controlled by a central processing unit (CPU) installed inside the digital camera. In the beginning, the lens moves back and forth around its original position (static position). As the lens moves, the CPU compares the image from the lens with the image in the image sensor. Finally, as the lens moves to the position where the image is the clearest, the lens stops at the position. In this case, the lens has to be continuously driven back and forth by a stepping motor. The stepping motor includes a cylinder-shaped stator with windings wound thereon, and a rotor received in the stator. The lens is received in the rotor. An internal thread is formed on an inner surface of the rotor, and an external thread screwed on the internal thread is formed on an outer surface of the lens. When a current is applied to the windings of the stator, the rotor is driven to rotate by the interaction of the alternating magnetic field established by the stator and the magnetic field of the rotor. The rotation of the rotor then turns to the axial telescopic movement of the lens through the interaction between the internal thread of the rotor and the external thread of the lens. At the moment when the CPU detects a clearest image as the lens moves back and forth, a stop signal is simultaneously sent to the motor. Therefore, the lens stops at the best focal position (static position).
However, the lens is directly threadedly driven by the rotor of camera; when the clearance of the threaded connection between the lens and the rotor is too large, the lens cannot be precisely driven by the rotor to the intended static position to have the best focus and clearest image. Such a shortcoming needs to be solved.